For a dealership I feel like there's less risk; they can do a quick background/credit check on you before accepting the personal check, and it's probably easier for them to track down someone who gives them a bad check. They also have better ability to absorb the loss, in the worst case. I'm sure they've modeled everything and have decided that taking personal checks is worth it financially to them.

(I remember reading long ago that if if a potential customer has to leave the dealership to go secure the proper form of payment, a significant percent just don't come back at all. They want to keep you there until you buy something, fairly standard sales tactic.)

But for a regular person just trying to sell their own car directly to someone else, they're absolutely going to want a cashier's check or cash. (Even the cashier's check can be risky; I doubt your average person is an expert in detecting a fraudulent one.)